1. Field of the Invention
The present invention relates to a light emitting display, and more particularly, to a light emitting display capable of compensating for threshold voltages of transistors and capable of having a plurality of organic light emitting diodes (OLED) that emit light through one pixel circuit.
2. Discussion of Related Art
Recently, various flat panel displays having weight and volume less than comparable cathode ray tube (CRT) displays have been developed. In particular, light emitting displays having high luminous efficiency, high brightness, wide view angle, and high response speed are in the limelight
An organic light emitting diode (OLED) has a structure in which an emission layer that is a thin film for emitting light is positioned between a cathode electrode and an anode electrode. Electrons and holes are injected into the emission layer so that they can be re-combined to generate exciters that emit light when their energies are reduced.
FIG. 1 illustrates a structure of a part of a conventional light emitting display. Referring to FIG. 1, four pixels are adjacent to each other and each pixel includes an OLED and a pixel circuit. The pixel circuit includes a first transistor T1, a second transistor T2, a third transistor T3, and a capacitor Cst. Each of the first, second, and third transistors T1, T2, and T3 includes a gate, a source, and a drain; and the capacitor Cst includes a first electrode and a second electrode.
Since the pixels have the same structure, only the pixel on the left top will be described in more detail. The source of the first transistor T1 is connected with a power source Vdd, the drain of the first transistor T1 is connected with the source of the third transistor M3, and the gate of the first transistor T1 is connected with a node A. The node A is connected with the drain of the second transistor T2. The first transistor T1 supplies a current corresponding to a data signal to the OLED.
The source of the second transistor T2 is connected with a data line D1, the drain of the second transistor T2 is connected with the node A, and the gate of the second transistor T2 is connected with a scan line S1. The second transistor T2 applies a data signal to the node A in accordance with a scan signal applied to the gate thereof.
The source of the third transistor T3 is connected with the drain of the first transistor T1, the drain of the third transistor T3 is connected with an anode electrode of the OLED, and the gate of the third transistor T3 is connected with an emission control line E1 to respond to an emission control signal. Therefore, the third transistor T3 controls the flow of a current that flows from the first transistor T1 to the OLED in accordance with the emission control signal to control emission of the OLED.
The first electrode of the capacitor Cst is connected with the power source Vdd, and the second electrode of the capacitor Cst is connected with the node A. The capacitor Cst stores charges in accordance with the data signal and applies a signal to the gate of the first transistor T1 by the stored charges for one frame so that the operation of the first transistor T1 is maintained for one frame.
However, according to the pixel used for the conventional light emitting display, since one OLED is connected with one pixel circuit, a plurality of pixel circuits are needed in order to emit light from a plurality of OLEDs so that a large number of the pixel circuits are needed.
Also, since one emission control line needs to be connected with a pixel row, the aperture ratio of the light emitting display deteriorates due to the emission control line.